1. Field of the Invention
The present invention is intended for use in a data processing system comprising several distributed processing units of different types which are connected to a remote central monitor and test station.
2. Description of the Prior Art
The remote simulation of commands normally available on the desk of a computer is important in several novel applications involving distributed systems, a typical example thereof being an automatic control system. The advantage of the use of a distributed system can be explained by the fact that the programmable and different functions are treated by each processing unit, connected at a distance, while the overall testing of the system may remain at the central monitor and test system which is connected to each of the distributed processing units by remote control.
The central station can monitor the status of each processing unit by transmitting the commands from the desk of a computer, or other test commands, for execution by the processing units, and by analyzing the results of the executed commands. These commands may be programmed at the central station and in such a case the periodic tests of the status of the processing units are automatically carried out; moreover, the operations based on an analysis of the tests can be automatically executed.
Several similar systems are known. One system describes the equipment for the execution of maintenance operations in a multiple processing system in which a special unit, comprising shift registers which are controlled by a central maintenance station, can be used for executing diagnostic tests. This necessitates connection of the maintenance unit to the processing unit via a special test bus. The diagnostic tests which can be performed using this technique are limited to the static commands for which the special unit has been manufactured. Another system describes the isolation of errors outside a data processing system by setting the relevant interface to a special test state, all communications originating from and going towards the interface being detoured to the simulation unit. Thus, the test state and the normal state of the system are two different states. A further system according to the present state of the art tests the peripheral units by switching to the test state in which the peripheral units are simulated by other devices.